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Philippine Trench
1952, 1975, while two, in 1911 and 1943 near eastern Mindanao, were slightly larger than the 2012 Samar earthquake. See also map below.|places= }} .]] The Philippine Trench (also Philippine Deep, Mindanao Trench, and Mindanao Deep) is a submarine trench to the east of the Philippines. The trench is located in the Philippine sea of the western North Pacific Ocean and continues NNW-SSE. It has a length of approximately and a width of about from the center of the Philippine island of Luzon trending southeast to the northern Maluku island of Halmahera in Indonesia. Immediately to the north of the Philippine Trench is the East Luzon Trench. They are separated, with their continuity interrupted and displaced, by Benham Plateau on the Philippine Sea Plate. Formation The Philippine trench is hypothesized to be younger than 8-9 million years ago. The central part of the Philippine fault formed during the Plio-Pleistocene times is considered to be an active depression of the earth’s crust. The trench formed from a collision between the Palawan and Zamboanga plates. This caused a change in geological processes going from a convergent zone to a subduction zone. The subduction zone is located west to east of the Philippine Islands. The rate of subduction on these plates is estimated to be about 15 cm per year. A convergent zone borders an estimate of 45% of the Philippine Trench today. Although there are vast areas of subduction zones, some authors have considered this region to have low seismic activity, though the USGS has recorded several earthquakes with magnitude ≥ 7.2 in the region as shown by the map to the side. Most recently, in 2012 the Philippine Trench experienced an earthquake of Mw 7.6. It hit the trench with a hypocenter depth of 34.9 km. Areas adjacent to the subduction zones however, have experienced large seismic activity. In 1897, northern Samar experienced a Ms 7.3 earthquake while in 1924 SE Mindanao experienced one with a Ms 8.2. Depth The trench reaches one of the greatest depth in the ocean, third only to the Mariana trench and the Tonga trench. Its deepest point is known as Galathea Depth and reaches 10,540 meters (34,580 ft) or (5,760 fathoms). At these depths, it is believed that deuterium, an isotope of hydrogen, resides near the bottom of the trench from deep-sea hydrothermal vents and is in high commercial interest. Sedimentation Sedimentation of the Philippine trench contains slightly metamorphosed, calc-alkalic, basic, ultrabasic rock and sand grains. The southern area of the trench contains homogenous, blue, clay silt and was poor in lime. Sand grains that were also found contained fresh basaltic andesite. The sediments found in the trenches are hypothesized to have been deposited by turbidity currents. A turbidity current is an underwater current that moves rapidly and carries sediment. Trenches in the Philippine region Known trenches are: * Manila Trench * East Luzon Trench * Philippine Trench * Negros Trench * Sulu Trench * Cotabato Trench References Category:Philippine Sea Category:Oceanic trenches of the South China Sea Category:Philippine tectonics Category:Subduction zones